Mechanical Properties of Hip Capsule Tissue After a Hip Arthroplasty

Total hip arthroplasty is a surgical procedure that replaces the hip joint by artificial materials. Here, the morphological and mechanical properties of the scar tissues that form around implants composed of either polymer and metal or ceramic are compared to native tissue removed during an initial total hip arthroplasty. Immuno-histological analyses of the samples showed different hierarchical structures of the tissues over three scales: the fiber, the fascicle and the tissue scales. At the tissue scale, micro-tensile tests were performed on millimetric samples and their non-linear elastic responses were identified by either an exponential law or an Ogden third-order constitutive model. At the fiber scale, a patient-specific micro-scale finite element model including the measured morphological parameters and the identified Ogden constitutive models for the fiber and for the matrix composed of a mixture of fibers in ground substance

Understanding the fundamental mechanisms of biofilms development and dispersal: BIAM (Biofilm Intensity and Architecture Measurement), a new tool for studying biofilms as a function of their architecture and fluorescence intensity

International audienceConfocal laser scanning microscopy (CLSM) is one of the most relevant technologies for studying biofilms in situ. Several tools have been developed to investigate and quantify the architecture of biofilms. However, an approach to quantify correctly the evolution of intensity of a fluorescent signal as a function of the structural parameters of a biofilm is still lacking. Here we present a tool developed in the ImageJ open source software that can be used to extract both structural and fluorescence intensity from CLSM data: BIAM (Biofilm Intensity and Architecture Measurement). This is of utmost significance when studying the fundamental mechanisms of biofilm growth, differentiation and development or when aiming to understand the effect of external molecules on biofilm phenotypes. In order to provide an example of the potential of such a tool in this study we focused on biofilm dispersion. cis-2-Decenoic acid (CDA) is a molecule known to induce biofilm dispersion of multiple bacterial species. The mechanisms by which CDA induces dispersion are still poorly understood. To investigate the effects of CDA on biofilms, we used a reporter strain of Escherichia coli (E. coli) that expresses the GFPmut2 protein under control of the nn.13P1 promoter. Experiments were done in flow cells and image acquisition was made with CLSM. Analysis carried out using the new tool, BIAM, indicates that CDA affects the fluorescence intensity of the biofilm structures as well as biofilm architectures. Indeed, our results demonstrate that CDA removes more than 35% of biofilm biovolume and suggest that it results in an increase of the biofilm's mean fluorescence intensity (MFI) by more than 26% compared to the control biofilm in the absence of CDA

Rhodamine B Doped ZnO Monodisperse Microcapsules: Droplet-Based Synthesis, Dynamics and Self-Organization of ZnO Nanoparticles and Dye Molecules

International audienceIn the present work, droplet-based microfluidics and sol-gel techniques were combined to synthesize highly monodisperse zinc oxide (ZnO) microspheres, which can be doped easily and precisely with dyes, such as rhodamine B (RhB), and whose size can be finely tuned in the 10-30 µm range. The as-synthesized microparticles were analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and confocal microscopy. The results reveal that the microspheres exhibit an excellent size monodispersity, hollow feature, and a porous shell with a thickness of about 0.6 µm, in good agreement with our calculations. We show in particular by means of fluorescence recovery after photobleaching (FRAP) analysis that the electric charges carried by ZnO nanoparticles primary units play a crucial role not just in the formation and structure of the synthesized ZnO microcapsules, but also in the confinement of dye molecules inside the microcapsules despite a demonstrated porosity of their shell in regards to the solvent (oil). Our results enable also the measurement of the diffusion coefficient of RhB molecules inside the microcapsules (D RhB = 3.8 × 10 −8 cm 2 /s), which is found two order of magnitude smaller than the literature value. We attribute such feature to a strong interaction between dye molecules and the electrical charges carried by ZnO nanoparticles. These results are important for potential applications in micro-thermometry (as shown recently in our previous study), photovoltaics, or photonics such as whispering gallery mode resonances

A detection based framework for systematic analysis of dual color TIRF microscopy

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Computational geometry-based scale-space and modal image decomposition application to light video-microscopy imaging

In this paper a framework for defining scale-spaces, based on the computational geometry concepts of a-shapes, is proposed. In this approach, objects (curves or surfaces) of increasing convexity are computed by selective sub-sampling, from the original shape to its convex hull. The relationships with the Empirical Mode Decomposition (EMD), the curvature motion-based scale-space and some operators from mathematical morphology, are studied. Finally, we address the problem of additive image/signal decomposition in fluorescence video-microscopy. An image sequence is mainly considered as a collection of 1D temporal signals, each pixel being associated with its temporal intensity variation

Change detection methods in fluorescence live cell imaging for sub-cellular trafficking analysis

International audienceThe study of membrane plasticity and the role of molecular "machines" in the control of biogenesis of the endo-cellular membranes have highlighted the crucial role of the "Rab" GTPases family as organizing centers of functional molecular platforms. Yet, to understand the regulation and coordination of these molecular assemblies, which are responsible for intracellular dynamic architectures, a more global vision, the development and the correlation of approaches at different spatial and temporal scales are needed. Considering the "fickle" nature of such dynamic architectures, the current performance of image acquisition systems and the analytical tools at our disposal, many technological challenges must be overcome. Dynamic aspects of perspectives described above require conceptual developments, particularly in the field of microscopy imaging. Moreover, to extract maximum information on the same sample, the development of an adapted microscopy, correlating different modalities, is needed. Last but not least, accurate image descriptors, allowing automatic detection and classification of molecular behavior in space and time, are indispensable. In this talk, we will focus on unsupervised change detection algorithms and new image modeling able to capture spatio-temporal regularities and geometries present in an image pair. In contrast to the usual pixel-wise methods and Markov Random Fields methods, we propose a patch-based formulation for modeling semi-local interactions and detecting local or regional changes in a microscopy image pair. By introducing dissimilarity measures to compare patches and binary local decisions, we design collaborative decision rules that use the total number of detections made by individual neighboring pixels, for different patch sizes. First, we will describe the patch-based representation for image pair analysis and present collaborative decision rules in neighborhoods. In addition, we will present the algorithm used to fuse binary decisions with statistical tests, at different spatial scales. Experimental results in video-microscopy (TIRF and wide-field imaging) demonstrate that the detection algorithm (with no optical flow computation) performs well at detecting meaningful changes and appearing/disappearing spots at the cell membrane. We also illustrate the approach for probabilistic local and global colocalization analysis of molecules in dual-color confocal images

A detection-based framework for the analysis of recycling in TIRF microscopy

International audienceEndocytosis/recycling and exocytosis are mechanisms conserved through evolution allowing cells to communicate with their external medium. In order to study these dynamic processes, the present work proposes a patch-based method for detecting recycling or exocytotic events at the Plasma membrane in fast TIRF microscopy combined with the computation of normalized temporal representations of those events. Evaluation, performed on TIRF sequences showing Transferrin receptor (TfR) recycling, validates a high detection rate fully compatible with an automatic data extraction and analysis of the plasma membrane recycling process

Impact of pulsed electric fields and mechanical compressions on the permeability and structure of Chlamydomonas reinhardtii cells

International audienceCurrent research findings clearly reveal the role of the microalga's cell wall as a key obstacle to an efficient and optimal compound extraction. Such extraction process is therefore closely related to the microalga species used. Effects of electrical or mechanical constraints on C. reinhardtii's structure and particularly its cell wall and membrane, is therefore investigated in this paper using a combination of microscopic tools. Membrane pores with a radius between 0.77 and 1.59 nm were determined for both reversible (5 kV•cm −1) and irreversible (7 kV•cm −1) electroporation with a 5 µs pulse duration. Irreversible electroporation with longer pulses (10 µs) lead to the entry of large molecules (at least 5.11 nm). Additionally, for the first time, the effect of pulsed electric fields on the cell wall was observed. The combined electrical and mechanical treatment showed a significant impact on the cell wall structure as observed under Transmission Electron Microscopy. This treatment permits the penetration of larger molecules (at least 5.11 nm) within the cell, shown by tracking the penetration of dextran molecules. For the first time, the size of pores on the cell membrane and the structural changes on the microalgae cell wall induced by electrical and mechanical treatments is reported

Stem cell derived osteocytes in situ characterization in bone-on-chip

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Microscopies synchrotron à SOLEIL

Le rayonnement synchrotron est un continuum d’énergie des infrarouges aux rayons X-durs. Avec l’amélioration des sources − une meilleure stabilité, une plus grande brillance, une plus faible divergence du faisceau et une meilleure cohérence − de plus en plus de lignes de lumière à travers le monde, et à SOLEIL en particulier, proposent des stations expérimentales dédiées à la microscopie